The trend in business and industry over the last several years has been toward housing said business or industry in much larger buildings, such as Wal-mart, K-mart, shopping centers, carpet mills and etc. Placing airconditioning units on the rooftop of such buildings is a very successful and convenient method of supplying conditioned air to such a facility, however these airconditioning units are subjected to continuous abuse by the load of work required and consequently need as much protection as possible. This invention contributes to the elimination of some of the airconditioning compressors from over heating, as the return air stream is filtered prior to its passing over the evaporator coils, thus preventing lent and dust buildup and reducing maintenance costs.